Given the form of an anharmonic, modified Ureyndash;Bradley molecular force field for AXnmolecules, it is shown how to express the mean vibrational displacements of bond lengths from equilibrium lengthsresimply in terms of elementary quantities. The dominant terms isolated are due to Morse stretching anharmonicity, nonbonded interactions, and the centrifugal stretching of bonds encountered as the atoms swing over arced trajectories in bending vibrations. Illustrative calculations are presented for CH4and CD4.
展开▼
